It was not a surprise to me that the professor did not want to discuss NNT , that is the amount of patents that needed to be treated with a MS drug for one person to benefit. The average NNT for a MS drug is about 5, this means that  4 out of 5 people taking the drug for years get no benefit, only side effects some times which can be fatal .The drug with the most promise  is Natalizumab with a NNT of 2. It was approved in 2004. It was withdrawn from the market  after it was linked with cases of the rare neurological condition  (PML) .However, twenty-four cases of PML had been reported since its reintroduction by October 2009, showing a sharp rise in the number of fatalities